Conventional air grilles generally comprise a rectangular metal frame and a number of parallel transverse blades rotatably mounted to the frame. The blades are generally secured by friction in a particular angular position with respect to the frame and to the flow of air.
Several embodiments of such typical grilles are disclosed in U.S. Pat. No. 4,103,601. However, conventional means for achieving a tight frictional fit between blade and the frame may suffer from one of two disadvantages. First, if the blade length is increased, for instance in the event that a wider air duct is used, the friction torques may be inadequate to resist the torque exerted on the blades by the pressure of the air moving in the duct. Consequently, the blade may be rotated away from the desired angular position. Second, a means for achieving an adequate frictional fit may be expensive to manufacture and install. For instance, the embodiments illustrated in FIGS. 1 to 3, 7, 8, and 15 to 23, of U.S. Pat. No. 4,103,601 all require costly cutting or stamping operations in their manufacture. In the case where a blade has been roll-formed from sheet metal into a generally hollow tubular shape, such cutting or stamping operations may be difficult, and thus even more expensive to complete. The manufacture of the grille assembly of some embodiments such as illustrated in FIG. 17, may require further operations. For example, the embodiment of FIG. 17 necessitates the bendng over of two tabs 38 to secure a blade in place. Any such additional installation operations further increase the cost of the assembly.
Similarly, the embodiment of FIG. 6 requires a metal support bar to be provided with plastic pins having frictional formations formed thereon. The formation of holes in the metal bar and the insertion of the pins into such holes are expensive operations. Also, the manufacture of frictional formations on the pins (as illustrated both in FIGS. 6 and 14) may require expensive dies. In order to achieve a satisfactory frictional fit, the tolerances for the dimensions of all (there are three illustrated) frictional formations must be carefully controlled.
The same frictional formations of FIGS. 6 and 14 may be subject to significant wear or deterioration when blades are fitted over the formations. Furthermore, the frictional formations increase the necessary blade thickness, thus reducing the free area of the grille through which air may flow. Alternatively, the diameter of the pins may be reduced to allow room for the frictional formations. However, the reduction in pin diameter may result in a loss of pin strength and durability. For these reasons, use of pins with frictional formations may not be desirable.
It is therefore desirable to provide a frictional blade assembly for an air grille in which the means for achieving a tight frictional fit is simple and inexpensive both to manufacture and to install.